Stripper construction for a perforator



y 1961 P. H. TAYLOR 2,983,176

STRIPPER CONSTRUCTION FOR A PERFORATOR Filed Aug. 21. 1956 H l 82 I 1INVENTOR. 82a WW RwZ/f. 72 20? 65 69 (21403625. Fiat United StatesPatent STRIPPER CONSTRUCTION FOR A PERFORATOR Paul H. Taylor, NorthTonawanda, N.Y., assignor to Tayco Developments, Inc., North Tonawanda,N.Y., a corporation of New York Filed Aug. 21, 1956, Ser. No. 605,245

1 Claim. (Cl. 83-138) This invention relates to self-contained punch andstripper combinations such as may be used in conventional dies forindividual 0 frame self-contained sub press dies for perforating sheetmetal or other materials.

Self-contained perforating units have been universally adopted byindustry for punching holes in sheet metal or the like, particularlywhere it is desired to punch a number of holes simultaneously.Individual perforating devices are ordinarily secured to a templet ormounted adjustably on bed rails in a press so that the perforators canbe located in a pattern corresponding to the pattern of holes which isto be punched and so that they can be actuated simultaneously by the ramof the press.

Perforating units of the type described ordinarily include both a punchand an aligned die together with work stripping means. Common devices ofthis type are disclosed in Wales Patent 1,955,866 and Wales Patent2,364,- 011. In these devices the downward Working stroke of the pressactuates a punch and at the same time stores energy in a wound steelWire spring which in turn actuates a stripper unit to strip theworkpiece from the punch when the press ram is raised.

Due to the large force required to Withdraw punch members from thickmetal stock, the capacity of perforating units is limited by thecapacity of the stripping device. When a large stripping spring isutilized, the overall width of the perforating'unit is increased, whichin turn limits the proximity of adjacent holes which can be punched in asingle perforating operation. Consequently, such units are frequentlyutilized with undersized, overloaded stripping springs With the resultthat early failure occurs. When adequate size coil stripping springs areutilized, they are of such a size that the perforating units cannot beused with standard presses having limited shut heights. Consequently, inorder to punch holes in material of more than Me of an inch inthickness, it has been necessary to utilize special types of punchpresses, and even with such machines a practical limit of inch workpiece thickness is encountered. As a result of these difliculties, twoor three operations have been necessary to punch hole patterns withrelatively close centers.

To overcome the deficiencies of perforating units utilizing mechanicalstripping springs, efiorts have been made to utilize compressible liquidor compressible solid devices to eflect the stripping. Units of thistype are disclosed in Taylor Patent 2,732,898 and Taylor Patent2,740,475. With perforating units of this type utilizing compressiblematerial stripping devices, it is possible to achieve greater strippingforces and to perforate material up to of an inch in thickness with thesame hole proximity as achieved with prior mechanical stripping springdevices. However, even these perforating devices have not been practicalfor most applications because of high cost and because of inherentdifficulties encountered by reason of use of conventional pistonarrangements in the stripping means.

In addition to the basic difiiculties encountered in prior perforatingdevices, several more specific difliculties have arisen. Ordinarilyself-contained perforators are reciprocably retained in closely fittedvertical apertures in the upper frame members of C frame units in themanner shown in Wales Patent 2,364,011 and Taylor Patent 2,740,475. Theperforator holder thickness adds to the overall width of the unit,thereby increasing the distance between hole centers which can besimultaneously punched. Ordinarily the holders are made of cast steel ora similar expensive, high strength material in order that the holderwall surrounding the punch will have the required high strength. Suchconstructions have precluded the use of thinner, lighter sections andlighter, lower strength materials such as aluminum or fiber glasscompositions. Furthermore, the holder aperture construction is notadapted to interchangeability With different punch assemblies so thatWhere different sized punches are required, diiferent holders must beprovided.

Where apertured holders are used with punch assemblies havingcompressible material stripping devices, another serious difliculty isencountered. In order that the punch be properly aligned 'm'th the die,close tolerance fit within the holder aperture is necessary. Since thecasing of a liquid spring or the like ordinarily expands one thousandthof an inch (.001") or more in diameter during a compression stroke, suchexpansion is sufiicient to cause seizing of the perforator assembly withthe '0 frame holder aperture. Consequently, prior compressible ma terialstripper devices have necessarily utilized relatively heavy casing wallthicknesses in order to prevent measurable expansion, thus eliminatingthe advantageous utilization of wall resiliency to increase the springefliciency. In addition, an increase in casing wall thickness furtherincreases the distance between hole centers which can be simultaneouslypunched.

To eliminate the various basic difiiculties in prior perforating devicesin which compressible material stripping means are utilized, the presentinvention provides a punch assembly containing a solid central punchmember and a tubular stripper which also acts as a liquid spring piston.A number of advantages flow from this type of construction. Among theseadvantages are simplification of the construction and operation of thepunch assembly, reduction of the cost of manufacture, reduction in thecompressive load on the punch shank, provision of additional support forthe punch end portion of the punch member, and simplification of thepunch member itself.

All of the specific difliculties encountered in utilizing aperturedholders are elirninated by the present invention which provides a closetolerance dovetail connection between the punch assembly casing and theupper arm of the '6 frame. Thus, there is no holder thickness to becontended with. Furthermore, the dovetail arrangement permits expansionof the spring chamber wall since it does not surround the Wall but isconnected to a relatively small portion of the periphery of the springchamber. In addition, C frame members of lighter construc tion, formedof less expensive and more easily fabricated materials, can be produced.

Where self-contained perforator units are directly connected with diesets, the present invention provides very much simplified means ofconnecting the ends of the punch assembly and the die block with matingsockets in the die sets.

It is an important object of the present invention to provide animproved self-contained punch and stripper combination for use inperforating materials.

Another object of the invention is to provide an improved perforatingunit embodying a liquid spring stripping means.

A further object of the invention is to provide a perforating unitcapable of punching larger holes on closer centers in thicker metal workpieces.

A still further object of the invention is to' provide a perforatingunit with a liquid spring stripper in which the stripper also acts asthe piston for the liquid spring.

Still another object of the present invention is to provide a liquidspring utilizing a tubular piston acting about a stem member whereby thestem member can be utilized as a perforating punch and the tubularpiston can be utilized as a work piece stripper.

An additional object of the invention is to provide improved means forconnecting a perforator unit punch assembly to a frame holder, wherebythe holder can be at least as narrow as the punch assembly, thuspermitting simultaneous formation of larger diameter holes on closercenters.

A related object is to provide improved means for connecting aself-contained punch and liquid spring stripper to a holder wherebyexpansion of the punch-stripper casing wall does not interfere withreciprocation of the punchstripper relative to the holder.

Another related object is to provide improved means for connecting aself-contained perforator to a holder to permit interchangeability ofdifierent sizes of perforators.

A kindred object is to provide improved perforator assembly connectingmeans whereby a single C frame can be utilized with varying perforatorsizes to permit punching a variety of hole sizes.

Other objects, features and advantages will be apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which.

The drawing is an enlarged fragmentary sectional view, partly inelevation. The invention is designed particularly for heavy dutypunching such as a diameter hole through a A thick plate.

The construction as shown in the drawing is particularly well suited forpunching and stripping metal thicknesses up to or for large diameterholes. It consists of a punch and die assemblage 80 comprising a punchstripper assembly '81 and a die 82 having pilot pins 81a and 82a,respectively, for engaging templates 84 and which will operatethestripper piston 90 upon removal of the punch 105' from the die 82. Theadvantages of a stepped tubular piston in a liquid spring are set forthin my co-pending application Serial No. 481,658, filed January 13, 1955,now Patent No. 2,909,368, dated October 20, 1959.

' One of the problems associated with liquid spring stripper punchcombinations is the variation in stripping loads relative to the grindlife on the punch. As the punch is 84 of a die set which are held inaccurate alignment through the leader pins (not shown) of a die set 85.Cap screws 88 and 89 engage pins 81a and 82a, respectively, to hold theparts on the templates.

The die member 82 has 21 dia aperture 82b and a slug chute 82c. Punchassemblage 81 consists of a casing 86 having stepped bores 87 and 88 forreceiving a stepped tubular piston 99 having an internal bore 92 in astepped tubular section 91. The bore 88 is of smaller diameter andconsequently receives the smaller diameter portion of the steppedtubular piston, as shown. A central punch piston closure member 109 hasa sturdy punch support body 101 terminating in enlarged heads 102 and163 at its opposite ends and having the general appearance of a spoolused for holding thread. The enlarged head 163 has a bore 194 forreceiving a punch insert 195 as will be noted in the drawing, theminimum diameter of the punch insert 105 is less than the minimumdiameter of the punch support body 161. A through-bolt 1% provides thepilot pin projection 81a and has a shoulder 167 for sealing the casing86 at 108. The bolt 106 has a bottom end portion threadedly insertedinto and holding a punch tip 1&5 at the lower end of the punch body 161.Thus, the bolt 106 takes the stripping loads on the punch tip 105. Amale seal 109 about the head 103 coacts with a male seal 110 about theupper end portion of the tubular stripping piston 90 to seal the insideand outside of the tubular piston. The tubular piston 90 provides a thinannular net piston area equivalent to the annular swept area between theseals but with a thick stepped tubular body of high strength. Theeffective piston area at the top of the stripper piston 90 is greaterthan the effective piston area at the bottom of the spool 161 so as toprovide a differential pressure in the punch 80 g ground, the springforce must be adjusted to the new length or designed oversize initiallyto accommodate grind life. I propose to accomplish this withoutadjusting the spring by providing a A" thick high strength plasticstripping pad 112 formed of nylon or the like, backed by a steel back upmember 113 through which the punch tip 105 extends. The nylon pad 112 isa tight fit on the punch 105 and the steel member 113 to exclude dustand dirt, and the construction is such that the end of the punch and thebottom face of the pad 112 are flush when the punch assembly isunactuated as shown. The stripper head assembly, comprising the nylonpad 112 and the back up member 113, may be secured to the lower end ofthe lower tubular section 91 in any suitable manner such as by beingpressed in the annular groove at the end of the piston section 91..Thus, the inexpensive molded or machined non-working stripper cap 112can be ground with the punch and at the same time will exclude dirt fromthe precision bore 92 during grinding operations. When a new punch tip105 is inserted, a new stripper cap 112 can be inserted using the formersteel back up member 113. In some instances, the steel back up member113 can be dispensed with as the nylon or plastic member 112 will havesufiicient rigidity itself.

The construction of this embodiment operates in the same manner as theprevious embodiments. The punch assembly 81 is moved downwardly toengage a flat sheet work piece (not shown) on the end of the die 82 andthereafter as the downward movement of the punch assembly continues, thepunch tip 105 perforates the work piece. The downward movement of thestripping piston is halted by the work piece, and as the punch continuesdownward, the liquid in the chamber 88 is compressed. After theperforating operation has been completed, the punch assembly is movedupwardly to retract From the foregoing discussion it Will be understoodthat the present invention provides a substantially improved perforatordevice in which a tubular liquid spring piston also acts as the workstripper for the perforator punch assembly. This construction makes itpossible to punch holes at least /1 of an inch in diameterin metalhaving a thickness of at least of an inch. By combining the stripper andthe liquid springpiston into a single member the construction is greatlysimplified. At the same time the life of the punch is lengthened becauseof the reduction in compressive force carried by the punch and becauseof the support for the punch end portion pro- ,vided by the tubularpiston. Where large holes are to be punched in thick metal, the tubularpiston-stripper is constructed in stepped form providing a rugged bodywith any desired spring rate. Precision attachment means are providedwhich provide for accurate retention of the punch assembly and themating die and at the same time allow ready interchangeability ofvarious punch sizes. Since the precision attachment means do notencircle the punch or die casings, the perforator sets may be placedcloser together to allow simultaneous punching of holes with minimumdistances between centers. Furthermore, the substantial freedom of thepunch assembly casing from attaching means permits limited casingexpansion to provide increased liquid spring efliciency and to elimi--nate necessity for thick casing walls which would cut down on theproximity of holes which can be simultaneously punched. Simplified punchgrinding is Provided for by adding a high strength plastic stripping padabout the punch end so that the punch and the pad can be groundsimultaneously while the pad prevents entry of foreign matter into thepunch. assembly.

Variations and modifications may be eitected without departing from thescope or" the novel concepts of the present invention.

1 claim:

A pertorator punch assembly adapted for utilizing a compressible liquidWork stripping means comprising a a cylindrical casing open at one end,the other end having a wall with a recessed opening therethrough, anaxial cylindrical chamber in said casing, 21 compressible liquid in saidchamber, an elongated punch support member coaxially mounted in andradially spaced from the walls of said punch support member, a punchmounted in a the punch support member recess and secured to saidthrough-bolt and extending out of the cylindrical chamber, said punchsupport member having a spool-shaped configuration, said cylindricalcasing having an ofiset inside said casing Wall portion, a tubularstripper disposed in the offset portion and having a portion closelyfitted 0 above the free end portion of said punch, the etfective pistonarea at the top of the stripper being greater than the effective pistonarea at the bottom of the spool, said stripper including a steppedtubular piston portion extending into and reciprocable in the spacebetween the punch support member and the cylindrical casing, firstliquid seal means formed on the outer surface of said tubular stripperin sealing engagement with the opposing wall of said cylinder, secondliquid seal means on the portion of the punch support member opposingthe inner surface of said tubular stripper and in sealing engagementtherewith, the maximum diameter of said spool being less than theminimum diameter of said chamber, whereby upon operation of the punch,the liquid is compressed thereby exerting a force against the etfectivepiston areas to cause the stripper to operate upon removal of the punchfrom a die.

References Cited in the file of this patent UNITED STATES PATENTS928,256 Grissom July 20, 1909 1,822,468 Wales Sept. 8, 1931 2,168,377Wales Aug. 8, 1939 2,191,826 Bath Feb. 27, 1940 2,432,804 Rieske Dec.16, 1947 2,674,311 Griswold Apr. 6, 1954 2,716,451 Taylor Aug. 30, 19552,867,276 Taylor Jan. 6, 1959

